• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Kirchhoff's Laws - Ohm's law - Resistance - Impedance

Extracts from this document...

Introduction

Resistance, property of any object or substance of resisting or opposing the flow of an electrical current. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit, according to Ohm's law. The unit of resistance is the ohm, the amount of resistance that limits the passage of current to one ampere when a voltage of one volt is applied to it. The standard abbreviation for electric resistance is R and the symbol for ohms in electric circuits is the Greek letter omega, Ω. For certain electrical calculations it is convenient to employ the reciprocal of resistance, 1/R, which is termed conductance, G. The unit of conductance is the mho (ohm spelled backwards) and the symbol is an inverted omega, .

The resistance of an object is determined by a property of the substance of which it is composed, known as the resistivity, and by the length and cross-sectional area of the object, and by the temperature. At a given temperature, the resistance is proportional to the object's resistivity and length, and inversely proportional to its cross-sectional area.

...read more.

Middle

Ohm's Law

Current flows in an electric circuit in accordance with several definite laws. The basic law of current flow is Ohm's law, named for its discoverer, the German physicist Georg Ohm. Ohm's law states that the amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive force impressed on the circuit and inversely proportional to the total resistance of the circuit. The law is usually expressed by the formula I = V/R, where I is the current in amperes, V is the electromotive force in volts, and R is the resistance in ohms (SeeElectrical Units). Ohm's law applies to all electric circuits for both direct current (DC) and alternating current (AC), but additional principles must be invoked for the analysis of complex circuits and for AC circuits involving inductances and capacitances.

A series circuit is one in which the devices or elements of the circuit are arranged in such a way that the entire current passes through each element without division or branching into parallel circuits.

...read more.

Conclusion

Impedance

The application of Ohm's law to circuits in which there is an alternating current is complicated by the fact that capacity and inductance are always present. Inductance makes the peak value of an alternating current lag behind the peak value of voltage; capacitance makes the peak value of voltage lag behind the peak value of the current. Capacitance and inductance inhibit the flow of alternating current and must be taken into account in calculating current flow. The current in AC circuits can be determined graphically by means of vectors or by means of the algebraic equation

image01.png

in which L is inductance, C is capacitance, and f is the frequency of the current. The quantity in the denominator of the fraction is called the impedance of the circuit to alternating current and is sometimes represented by the letter Z; then Ohm's law for AC circuits is expressed by the simple equation I = E/Z.[2]


[1]

[2]

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. Peer reviewed

    Measurement of the resistivity of Nichrome

    5 star(s)

    result for Wire A and Wire B is nearly the same, but the result for Wire B is more accurate than that for Wire A. As the uncertainty is calculated by both uncertainty of cross-sectional areas and uncertainty of gradients which depend on the diameters (gradients depend on Error bar which worked out by diameters).

  2. Investigating the Capacitance of a Parallel-Plate.

    We connect the parallel-plate capacitor to four batteries, i.e. 5.8V and this is unchanged during the whole investigation. Results: N 1 2 3 1 0.5 0.333 I / 0.94 ± 0.01 0.50 ± 0.01 0.35 ± 0.01 The graph of I against is drawn on a separate graph paper and is attached on the next page.

  1. Investigating Ohms law

    Current (mili amps) Voltage (V) Current (mili amps) Voltage (V) Current (mili amps) Average voltage (V) Average current (mili amps) 0 0 0 0 0 0 0 0 2 6.00 2 5.10 2 6.60 2 5.90 3 8.60 3 7.30 3 8.90 3 8.27 4 11.30 4 9.70 4 11.70 4 10.90 5 14.20 5

  2. Physics - Resistivity

    I took the readings on intervals according to the value of voltage I was given, and kept the electromotive force the same, on 12. As it is on 12, the power pack would heat up rapidly, and because I don't want it to overheat, I have to keep on turning the power pack off between readings.

  1. Investigating the capacitance of a parallel report

    We may say that one plate and earth or another conductor form an extra capacitor. In fact, any two materials can form a capacitor which can store charges. Hence, it's a major source of errors. It is assumed that edge effect of the plates can ignored and all field lines between the plates are straight.

  2. Characteristics of Ohmic and Non Ohmic Conductors.

    supply has to be applied to the circuit. The connections can be anyway, positive and negative or negative and positive. We should still get a straight line through the origin. This is one of the characteristics of ohmic conductors. The rheostat will be used to vary the current.

  1. Ohm's law

    However, not all objects obey Ohm's Law. Those which do are called Ohmic Conductors, whereas those that disobey Ohm's Law are called Non-ohmic Conductors. Circuit Diagram: 390?

  2. Coursework To Find The Internal Resistance Of A PowerSupply

    I decided not to change the resistance setting on the rheostat while the power pack is continuously running but in order to maintain the same, constant, temperature of the power pack, it will be switched on to take the results and then switched off.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work